Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
There is known screening that transforms an image into a halftone dot image using a screen such as a halftone screen and a line screen. The halftone dot image is constituted of periodic arrays of halftone dots expressed in tones. For execution of appropriate screening, in the screening, according to an attribution of the image before transformation, various parameters such as a mesh pattern (screen pattern), a screen line width, and a screen angle in the screening are set.
If the screening is performed on a character of light print density and a thin line, an interval between the halftone dots become large. Accordingly, a portion where the halftone dot is not arranged is generated at a part of an edge of the thin line in the halftone dot image or the character. As a result, a white void and a break may be seen at the character and the thin line.
Therefore, there is known the following method. A character and an edge part of a line are detected. According to attributions of the character and the line, one matrix is selected among a plurality of threshold matrixes of different growth methods and outputs the image.